We will continue our investigations of the regulatory mechanisms used by Tetrahymena pyriformis cells to control the physical state of their membranes. These studies largely center on the regulation of membrane fluidity by altering pathways of lipid metabolism. By perturbing fluidity through the use of chemicals, temperature changes, etc., the metabolic response to the cell will be measured. The changing physical state of the various functionally different membranes will be measured by fluorescence depolarization techniques and be examining freeze fracture electron microscopy replicas. The effects of acclimation to cations, anesthetics, and ethanol upon membrane properties will be measured as will the changes in membrane properties during the cell division cycle in synchronized cultures.